Methods of tissue heart valve assembly

ABSTRACT

Improved, adaptable tissue-type heart valves and methods for their manufacture are disclosed wherein a dimensionally stable, pre-aligned tissue leaflet subassembly is formed and its peripheral edge clamped between and attached to an upper shaped wireform and a lower support stent. A variety of adaptable structural interfaces including suture rings, flanges, and conduits may be attached to the support stent with or without an outlet conduit disposed about the wireform to provide a tissue-type heart valve adaptable for use in either a natural heart or in mechanical pumping devices. The methods include forming individual leaflets with a template and using the template to attach the leaflets together to form a tissue leaflet subassembly. The template and leaflets include a straight edge terminating in oppositely directed tabs, and a curvilinear cusp edge extending opposite the straight edge. The template may include a guide slot in its straight edge and the assembly includes aligning two leaflet tabs with the template and passing sutures through the guide slot and through the leaflet tabs. The leaflet subassembly is mated to a wireform with the tabs extending through commissure posts of the wireform. A support stent having an upper surface matching the lower surface of the wireform sandwiches the edges of the leaflet subassembly therebetween. Separated tabs on the leaflet subassembly are passed through the wireform commissures and attached to adjacent stent commissures so as to induce clamping of the leaflet tabs between the stent commissures and wireform commissures upon a radially inward force being applied to the leaflets.

RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. applicationSer. No. 08/826,408, filed Mar. 27, 1997, entitled "Tissue Heart Valveswith Subassemblies," and now U.S. Pat. No. 5,928,281.

FIELD OF THE INVENTION

The present invention is directed to tissue-type prosthetic heart valvesand to improved methods of making such valves.

BACKGROUND OF THE INVENTION

Prosthetic heart valves are used to replace damaged or diseased heartvalves. In vertebrate animals, the heart is a hollow muscular organhaving four pumping chambers: the left and right atria and the left andright ventricles, each provided with its own one-way valve. The naturalheart valves are identified as the aortic, mitral (or bicuspid),tricuspid and pulmonary valves. Prosthetic heart valves can be used toreplace any of these naturally occurring valves. Two primary types ofheart valve replacements or prostheses are known. One is amechanical-type heart valve that uses a pivoting mechanical closure toprovide unidirectional blood flow. The other is a tissue-type or"bioprosthetic" valve which is constructed with natural-tissue valveleaflets which function much like a natural human heart valve, imitatingthe natural action of the flexible heart valve leaflets which sealagainst each other or coapt between adjacent tissue junctions known ascommissures. Each type of prosthetic valve has its own attendantadvantages and drawbacks.

Operating much like a rigid mechanical check valve, mechanical heartvalves are robust and long lived but require that valve implant patientsutilize blood thinners for the rest of their lives to prevent clotting.They also generate a clicking noise when the mechanical closure seatsagainst the associated valve structure at each beat of the heart. Incontrast, tissue-type valve leaflets are flexible, silent, and do notrequire the use of blood thinners. However, naturally occurringprocesses within the human body may attack and stiffen or "calcify" thetissue leaflets of the valve over time, particularly at high-stressareas of the valve such as at the commissure junctions between the valveleaflets and at the peripheral leaflet attachment points or "cusps" atthe outer edge of each leaflet. Further, the valves are subject tostresses from constant mechanical operation within the body.Accordingly, the valves wear out over time and need to be replaced.Tissue-type heart valves are also considerably more difficult and timeconsuming to manufacture.

Though both mechanical-type and tissue-type heart valves must bemanufactured to exacting standards and tolerances in order to functionfor years within the dynamic environment of a living patient's heart,mechanical-type replacement valves can be mass produced by utilizingmechanized processes and standardized parts. In contrast, highly trainedand skilled assembly workers make tissue-type prosthetic valves by hand.Typically, tissue-type prosthetic valves are constructed by sewing twoor three flexible natural tissue leaflets to a generally circularsupporting wire frame or stent. The wire frame or stent is constructedto provide a dimensionally stable support structure for the valveleaflets which imparts a certain degree of controlled flexibility toreduce stress on the leaflet tissue during valve closure. Abiocompatible cloth covering on the wire frame or stent provides sewingattachment points for the leaflet commissures and cusps. Similarly, acloth covered suture ring can be attached to the wire frame or stent toprovide an attachment site for sewing the valve structure in positionwithin the patient's heart during a surgical valve replacementprocedure.

With over fifteen years of clinical experience supporting theirutilization, tissue-type prosthetic heart valves have proven to be anunqualified success. Recently their use has been proposed in conjunctionwith mechanical artificial hearts and mechanical left ventricular assistdevices (LVADs) in order to reduce damage to blood cells and theassociated risk of clotting without using blood thinners. Accordingly, aneed is developing for a tissue-type prosthetic heart valve that can beadapted for use in conjunction with such mechanical pumping systems.This developing need for adaptability has highlighted one of thedrawbacks associated with tissue-type valves--namely, the time consumingand laborious hand-made assembly process. In order to provideconsistent, high-quality tissuetype heart valves having stable,functional valve leaflets, highly skilled and highly experiencedassembly personnel must meticulously wrap and sew each leaflet and valvecomponent into an approved, dimensionally appropriate valve assembly.Because of variations in tissue thickness, compliance and stitching,each completed valve assembly must be fine tuned using additionalhand-crafted techniques to ensure proper coaptation and functionallongevity of the valve leaflets. As a result, new challenges are beingplaced upon the manufacturers of tissue-type prosthetic valves in orderto meet the increasing demand and the increasing range of uses for theseinvaluable devices.

Accordingly, consistent with the developing practice of the medicalprofession, there is a continuing need for improved tissue-typeprosthetic heart valves which incorporate the lessons learned inclinical experience, particularly the reduction of stress on the valveleaflets while maintaining desirable structural and functional features.Additionally, there is a growing need for improved tissue-typeprosthetic heart valves which can be adapted for use in a variety ofpositions within the natural heart or in mechanical pumps, such asartificial hearts or ventricular assist devices, as well as alternativelocations in the circulatory system. Further, in order to addressgrowing demand for these devices, there is a need for tissue-type heartvalves that are simpler and easier to manufacture in a more consistentmanner than are existing valves.

SUMMARY OF THE INVENTION

Directed to achieving the foregoing objective and to remedying theproblems in the prior art, disclosed herein are novel tissue heart valveconstructions and components thereof, and simplified methods offabricating the same. The improved tissue heart valves of the presentinvention are fabricated to include standardized leaflet structuresubassemblies that can be modified readily to adapt to differentintended applications. Of equal importance, the leaflet structuresubassemblies uniformly distribute tensile loads along the entireperipheral leaflet cusp, reducing stress points and significantlyimproving the long-term functionality of the valve assembly. As an addedbenefit of the present invention, the stability and adaptability of thetissue valve subassembly is achieved through simplified manufacturingprocesses utilizing fewer steps and subassemblies. This manufacturingprotocol can be incorporated into branched, adaptable manufacturingtechniques for the production of tissue heart valves having a variety ofend uses. Further, these improved construction techniques expedite theoverall manufacturing process and improve the consistency of the tissuevalves so produced while simultaneously reducing the need forpost-assembly fine tuning and quality-control procedures.

According to one aspect of the present invention, a tissue-type heartvalve includes a dimensionally stable, pre-aligned tissue leafletsubassembly, a generally circular wireform, and a generally circularsupport stent. The wireform has a bottom surface dimensioned to receivethe pre-aligned tissue leaflet subassembly in fixed, mating engagement.The support stent has an upper surface dimensioned to seat and fix inmeeting engagement with the prealigned tissue leaflet subassembly whichis fixedly disposed in mating engagement with the bottom surface of thewireform.

Pursuant to this construction, an exemplary tissue valve includes aplurality of tissue leaflets that are templated and attached together attheir tips to form a dimensionally stable and dimensionally consistentcoapting leaflet subassembly. Then, in what is essentially a singleprocess, each of the leaflets of the subassembly is aligned with andindividually sewn to a cloth-covered wireform, from the tip of onewireform commissure uniformly, around the leaflet cusp perimeter, to thetip of an adjacent wireform commissure. As a result, the sewed suturesact like similarly aligned staples, all of which equally take theloading force acting along the entire cusp of each of the pre-aligned,coapting leaflets. The resulting tissue-wireform structural assemblythereby formed reduces stress and potential fatigue at the leafletsuture interface by distributing stress evenly over the entire leafletcusp from commissure to commissure. This improved, dimensionally stable,reduced-stress assembly is operatively attached to the top of apreviously prepared cloth-covered stent to clamp the tissue leafletcusps on a load-distributing cloth seat formed by the top of thecloth-covered stent without distorting the leaflets or disturbing theirrelative alignment and the resultant coaptation of their mating edges.

The stent is secured to the assembly with the commissures of the stentextending up into the corresponding commissures of the leaflet, wireformassembly. The stent itself can be formed of an inner polyester filmsupport secured to a surgically acceptable metal ring such as anElgiloy™ metal stiffener having a cloth cover cut, folded and sewnaround the support and stiffener combination. Alternatively, instead ofhaving an Elgiloy outer band and a laminated polyester film support, thetwo stent layers can both be polyester layers or a single piece stenthaving appropriately flexible commissure posts. Either stentconstruction provides support and dimensional stability for the valvestructure extending from commissure to commissure and being evenlydistributed around each leaflet. This assembly methodology allows theevenly sutured tissue of the leaflet cusps to be sandwiched between thewireform and the stent and to thereby further distribute the loadingforces more evenly around the attachment site. Because the tissueleaflets experience lower, more evenly distributed stresses duringoperation, they are less likely to experience distortion in use. Thus, amore stable, long lived, functional closure or coaptation of theleaflets is provided by this even distribution of attachment forces.

A number of additional advantages result from the present invention andthe stent construction utilized therein. For example, for each key areaof the stent, the flexibility can be optimized or customized. Ifdesired, the coapting tissue leaflet commissures can be made more orless flexible to allow for more or less deflection to relieve stresseson the tissue at closing or to fine tune the operation of the valve.Similarly, the base radial stiffness of the overall valve structure canbe increased or decreased to preserve the roundness and shape of thevalve.

Unlike a rigid mechanical valve, the stent does not act as a rigid heartvalve structure but as a radially stable, yet axially flexible support.A rigid structure is unnecessary by utilizing the teachings of thepresent invention because the valve leaflets are dimensionallypre-aligned along their mutually coapting mating or sealing edges priorto being directly attached to the base of the cloth-covered wireform. Asa result, the entire sealing aspect of the valve can be aligned in threedimensions at once without the variability previously experienced in theconstruction of prior art tissue-type valves. In addition to eliminatingthe need for post-assembly adjustment, this pre-alignment provides forconsistency and simplicity in the manufacture of the valve structure.Further, the wireform functions as a template for suturing the leafletcusps to the valve subassembly with uniform stitching from commissuretip to commissure tip. This produces a dimensionally consistentstructure that can interface with the stent in a previously unobtainableuniform manner. The consistent dimensional integrity of the leafletwireform subassembly enables the stent to function as a stress relievingsupport clamp which further secures the leaflet cusps in the valvestructure to provide an added degree of stability and stressdistribution. If desired, providing the top of the stent with a singleor double fold of covering cloth provides the stent lip with adeformable cloth seat that assists in the distribution of load aroundthe leaflet cusps and simplifies sewing the stent to the tissue leafletwireform subassembly. Those skilled in the art will appreciate thatattaching the stent to the tissue leaflet wireform functions tostabilize the projecting commissure posts of the valve subassemblywithout stiffening their desirable axial flexibility. This novelconstruction technique eliminates the need for separate commissure postsat the tissue leaflet commissures and also eliminates multiple tissueand cloth layers at the wireform commissure posts which adds touniformity and consistency in valve production and eliminates assemblysteps. As a result, valve manufacture is not only improved, but alsosimplified and expedited as well.

The stent also functions as an adaptable structural interface, allowingthe tissue-wireform-stent structural subassembly to be attached to avariety of additional structures dependent upon intended valve placementand operating environments. For example, with the supporting stentsecured to the tissue-wireforn structural assembly, the resulting valveassembly can be attached to, for example, a suture ring, a flange or aconduit depending on the desired valve application. To form a conduitvalve, the suture ring can be attached directly to the inflow or base ofthe stent to enable the implanting surgeon to sew the valve in placewithin the heart. Alternatively, when the valve is to be used forartificial hearts or for left ventricular assist devices (LVADs), a morerigid flange can be attached to the stent inflow to function as amechanical mount. In some circumstances it may be desirable to form aconduit valve wherein flexible or rigid conduits are required to replacea missing portion of a patient's aorta or to interface with anartificial blood pumping device. In such circumstances, an inlet conduitmay be attached to the stent inflow and, if desired, a correspondingoutflow conduit can be attached inside or outside of the valve wireform.Unlike prior art tissue heart valves, the present invention providesthis flexibility and adaptability of use because key valve componentscan be standardized for different types of valves or valve applications.This manufacturing and structural consistency also improves qualitycontrol and provides repeatability and consistency in the formation ofthe valves. It also simplifies final assembly that in turn provides forincreased production rates without sacrificing consistent productquality.

More specifically, as part of the flexibility of the present invention,the stent is designed to be adaptable so that different ways ofattaching the valve to its various intended applications can beaccommodated. The novel construction that allows for this universalapplication results from the stent providing a complete uniform supportto the dimensionally stable, pre-aligned wireform/leaflet subassembly.Because of this adaptability, the valve of the present invention canfunction in a variety of applications, including that of a temporaryheart valve prosthesis within a circulatory support system using arelatively rigid flange or a conduit assembly rather than a standardsoft sewing ring. Alternatively, the present invention can function as aprosthetic valve having a soft, scallop-shaped sewing ring for aorticpositioning or a soft flat sewing ring for mitral positioning, or as aconduit valve by incorporating proximal and distal conduits attached onboth the inflow and outflow valve ends. The outflow conduit can have asinus shape to improve blood flow if desired. Within an artificial heartsystem, the valve of the present invention mimics the hemodynamicpumping action of the heart while sustaining the patient until a donorheart is located and successfully transplanted. In this application,both blood inflow and outflow functions can be accommodated by thepresent invention.

Other objects and advantages of the present invention will become moreapparent to those persons having ordinary skill in the art to which thepresent invention pertains from the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an exemplary heart valve ofthe present invention illustrating the assembly relationship of thestandardized components and alternative valve attachment applicationstructures;

FIG. 2 is a perspective view illustrating the step of templating andtrimming exemplary leaflets used in making a tissue heart valve of thepresent invention;

FIG. 3 illustrates the initial steps of templating and pre-aligning theleaflets of the valve subassembly;

FIG. 4 shows additional steps in the pre-alignment of the valve leafletsubassembly;

FIG. 5 is an enlarged view illustrating an exemplary attachment step ofthe pre-aligned leaflets to a wireform commissure tip;

FIG. 6 is a perspective view illustrating the subsequent preliminaryattachment of the exemplary leaflet cusps to the wireform of FIG. 5;

FIG. 7 is a perspective view illustrating the uniform attachment of theperimeter cusps of leaflets to the cloth covered wireform;

FIG. 8 is an enlarged view of one of the pairs of attached leaflet tabsof FIG. 7 illustrating the uniform attachment of the cusps to thewireform commissure tip;

FIG. 9 is a perspective view illustrating the attachment of theexemplary tissue leaflet-wireform structural subassembly to an exemplarystent of the present invention;

FIG. 10 is an enlarged view of one of the pairs of leaflet tabs of FIG.9 illustrating a further attachment step of the stent to the wireform atthe commissure tip, clamping the leaflet cusps therebetween;

FIG. 11 is an enlarged view of one of the commissure tips of thetissue-wireform structural assembly of FIG. 10 illustrating the clampingof the leaflets by the stent;

FIG. 12 is a perspective view illustrating a final attachment step ofthe exemplary tissue-wireform structural assembly to the stent;

FIG. 13 is an enlarged view taken on circle 13 of FIG. 12 illustratingadditional exemplary attachment techniques;

FIG. 14 is an enlarged view taken on circle 14 of FIG. 12 illustratingadditional exemplary attachment techniques;

FIG. 15 is a perspective view illustrating an exemplary attachment stepof the tissue leaflet tabs at the commissure tip;

FIG. 16 is a view similar to FIG. 15 illustrating an alternativeattachment step;

FIG. 17 is an exploded perspective view illustrating an exemplarymulti-piece stent formed of a flexible support and an associatedstiffener of the present invention;

FIG. 18 is a perspective view illustrating the attachment of the supportto the stiffener of FIG. 17;

FIG. 19 is a perspective view illustrating an initial step in thecovering of the stent components of FIG. 18 with cloth;

FIG. 20 is an enlarged view of the top of FIG. 19 illustratingadditional steps in the attachment of the cloth to the stent components;

FIG. 21 is a perspective view illustrating additional steps offabricating sewing tabs for attaching the cloth to the stent components;

FIG. 22 is an enlarged view of a portion of FIG. 20 illustratingsubsequent fabrication steps;

FIG. 23 is an enlarged cross-sectional view taken on line 23--23 of FIG.22;

FIG. 24 is a view similar to FIG. 22 illustrating additional fabricationsteps;

FIG. 25 is a perspective view of the cloth-covered stent of FIG. 18illustrating the cloth seating lip;

FIG. 26 is an enlarged cross-sectional view on line 26--26 of FIG. 25illustrating additional aspects of the fabrication of the exemplarystent assembly;

FIG. 27 is a perspective view illustrating initial components of anexemplary suture ring of the present invention;

FIG. 28 is an enlarged cross-sectional view illustrating aspects of thefabrication of the exemplary suture ring;

FIG. 29 is a perspective view illustrating additional features of theexemplary suture ring assembly;

FIG. 30 is an enlarged sectional view of a portion of FIG. 29illustrating additional aspects of the fabrication of the suture ringassembly;

FIG. 31 is an enlarged sectional view illustrating additional aspects ofthe finished exemplary suture ring assembly;

FIG. 32 is an exploded perspective view illustrating positioning andassembly of a suture ring and leaflet subassembly configuration;

FIG. 33 is a top perspective view illustrating additional suture ringleaflet subassembly attachment steps;

FIG. 34 is a bottom perspective view illustrating further exemplarysuture ring attachment steps;

FIG. 35 is a cutaway perspective view illustrating an exemplaryattachment of an outflow conduit to an exemplary valve of the presentinvention;

FIG. 36 is an enlarged cross-sectional view illustrating additionalaspects of the conduit attachment;

FIG. 37 is a cross sectional view similar to FIG. 36 illustratingalternative conduit attachment features; and

FIG. 38 is an exploded perspective view illustrating additional valveattachment alternatives of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring more particularly to the drawings, FIG. 1 is an explodedassembly view, illustrating exemplary alternative embodiments of animproved, adaptable tissue valve 50, its individual components, and itsalternative configurations produced in accordance with the teachings ofthe present invention. Valve 50 includes a pre-aligned, standardizedleaflet subassembly 52, a cloth-covered wireform 54 and a support stent56. As will be discussed in detail below, during assembly of valve 50,the pre-aligned leaflet subassembly 52 and the cloth-covered wireform 54are first assembled in accordance with the present invention to form atissue-wireforn structural assembly 58 (see FIGS. 2 to 9). Then, thestructural assembly 58 is secured to stent 56 to form the assembledvalve 50.

As illustrated FIG. 1, valve 50 is uniquely configured to enableproduction of several useful alternative valves for a variety of end-useapplications. For example, if the desired application is the replacementof a native heart valve, valve 50 can be attached to a relatively softsuture ring 60 for subsequent sewing into place within a heart (notshown). Alternatively, if it is desired to use valve 50 in a leftventricular assist device (LVAD) or in a mechanical heart pump, valve 50can be mounted to an appropriately rigid mechanical flange 62. Further,in both natural and mechanical applications where it is desirable toincorporate a conduit, valve 50 may be attached to either an inflowconduit 64 and/or an outflow conduit 66.

Production of the Tissue-Wireform Structural Assembly

In the present disclosure, exemplary valve 50 is illustrated as athree-leaflet or tricuspid valve. However, it will be appreciated bythose skilled in the art that valve 50 may be configured to have twoleaflets or any other desired leaflet configuration depending on theintended application.

A first step in the assembly of tissue valve 50 is the attachment oftissue leaflets 68 to one another to form a consistently dimensioned,standardized leaflet subassembly. Tissue leaflets are typically formedfrom pericardial, porcine or similar tissue obtained from donor organs,which tissue is preserved or "fixed" prior to use in assembling a valve.Those skilled in the art will appreciate that the dimensions of leafletsubassembly 52 will vary depending upon the intended end use andassociated positioning and dimensional requirements of the finishedvalve. However, pre-alignment and stitching in accordance with theteachings of the present invention not only simplifies the manufactureof valve 50 but also functions to align the entire valve mating orseating surfaces at once. This eliminates variations in leafletalignment and dimensional relationships and significantly minimizes theneed to adjust the tissue leaflets after final assembly of the valve inorder to ensure proper coaptation at the mating edges of the leaflets.

Referring now to FIG. 2, the desired number of tissue leaflets 68 (inthis example, three leaflets) are obtained from natural tissue as knownin the art, and each leaflet 68 is trimmed to the appropriate desiredshape and size for the intended valve use using template 69, defining agenerally straight or linear coapting mating edge 70 having opposingends 71, 72 and a generally arcuate peripheral cusp 73 extendingtherebetween. More particularly, each leaflet 68 is placed on a cuttingboard 74 and the selected template 69 is then placed over the leaflet68. Tissue 75 extending beyond the boundaries of template 69 is then cutaway using a sharp razor blade 76 or similar cutting tool.

A characteristic of pericardial tissue is that one surface is smootherthan the opposite surface. Accordingly, it is desirable that the lesssmooth surface be identified to serve as the mating surface at edge 70with an adjacent leaflet edge 70. After the leaflets 68 are trimmed andthe mating surfaces identified, two of the leaflets 68a, 68b arepre-aligned or mated together along with template 69 as shown in FIG. 3.The two leaflets 68a, 68b are then attached or stitched together at oneend 71 to define the first in a plurality of pairs of aligned, matingleaflet ends. For example, a needle that has been "double-threaded,"that is, needle 78 that has been threaded with a looped (or "folded")segment of thread 80 is inserted and pushed through the leaflets 68a,68b at the location dictated by guide slot 82 at one end of template 69.Template 69 may then be removed, with needle 78 being brought over thetop of leaflets 68a, 68b and passed back through the loop and pulledtightly. Naturally, alternative attachment methods or stitches may beutilized within the scope and teaching of the present invention. Theopposite ends 72 of the first two leaflets 68a, 68b of the exemplarythree leaflet valve are not sewn together at this time.

Referring now to FIG. 4, a third leaflet 68c is pre-aligned and attachedto the other two leaflets 68a, 68b in a tricuspid format, again usingtemplate 69. In particular, third leaflet 68c is mated with template 69,and the respective unsewn ends 72 of the first two leaflets 68a, 68b arespread out and then aligned with the respective opposite ends 71, 72 oftemplated third leaflet 68c. Again using guide slot 82 of the template69 as a guide, a double-threaded needle with thread 80 is insertedthrough each of the unsewn pairs of the three leaflets 68a, 68b, 68c tosecure the leaflet ends together in pairs as shown. The template maythen be removed, and, for each stitch, needle 78 may be brought over thetop of leaflets 68a, 68b, 68c and passed back through the loop andpulled tightly to produce leaflet subassembly 52 having three leafletmating ends.

Referring now to FIGS. 5 and 6, it is preferred to attach leafletsubassembly 52 to the underside or bottom 83 of wireform 54. Exemplarywireform 54 is a wire reinforced cloth having a cloth edge 84 and isshaped in a manner substantially conforming to the shape of the leafletsubassembly structure 52. In the embodiment shown, wireform 54 isgenerally circular in shape and has a sinusoidal undulation defining aplurality of commissure tips 86 corresponding to the pairs of leafletmating ends. The cloth of wireform 54 includes the circumferential clothedge 84 that serves as a sewing or attachment surface for the leafletsubassembly 52. Exemplary wireform 54 includes the three raisedcommissure tips 86 which receive the three respective pairs of attachedmating ends of leaflets 68a, b, and c of the pre-aligned leafletsubassembly 52.

An exemplary technique for attaching the leaflet pairs at an end of theleaflet subassembly 52 to one of the commissure tips 86 of wireform 54is shown in FIG. 5. Needle 78 (not shown) with looped thread 80, whichwas used to sew the leaflet ends together, is inserted up from leaflets68 (as shown in dashed lines), through an inner edge of cloth edge 84 asindicated at 87, so that the top surfaces of mating leaflets 68 aresecured into contact with wireform 54. The needle is then re-insertedthrough an outer edge of and from underneath cloth edge 84 as indicatedat 88', and a first lock 89, preferably a single lock stitch, is madewith thread 80. The locking process can be repeated as indicated at 88"with a second lock 90, preferably a double lock stitch. Finally, theneedle can be inserted into the middle of and from underneath cloth edge84 as indicated at 91 and the thread pulled so that first and secondlocks 89, 90 are pulled underneath cloth edge 84 and thereby hidden andprotected during the remaining fabrication process. The excess thread isthen trimmed and discarded. This method is repeated for securing each ofthe respective pairs of attached, aligned mating leaflet ends of matedleaflets 68a, 68b, 68c of subassembly 52 to the respective commissuretips 86 of wireform 54. Thus, wireform 54 functions as an additional,permanent template for positioning the leaflet commissures in theirfinal position relative to one another. As an added benefit of thepresent invention, this manufacturing technique further stabilizes theposition of the coapting valve leaflets relative to one another prior toattachment of the leaflet cusps to the wireform. Thus, it is possible toattach the entire peripheral leaflet cusp uniformly from the tip of onecommissure to the next in order to produce consistent attachment stressalong the leaflet edge.

Referring now to FIGS. 6 and 7, the next exemplary step for securing theexemplary leaflet subassembly 52 to wireform 54 is to attach peripheralcusps 92 of each of the leaflets 68 to cloth edge 84. In thatconnection, slip knots 94 (i.e., knots that may be undone) are spacedperiodically along wireform 54 to temporarily fit leaflet cusps 92 inposition on wireform 54. Three of the slip knots 94 may be made for eachleaflet cusp 92, with one at the center of the cusp and two at points ofinflection with the commissures, as this helps to uniformly stabilizethe cusp in position during attachment to wireform 54.

As shown in FIGS. 7 and 8, temporarily secured leaflet cusps 92 then areattached to wireform cloth edge 84, preferably using double-threaded"in-and-out" sutures 96, starting from a center position 98 of eachleaflet cusp 92 and running to the tips of each commissure 86. At aboutone millimeter from the commissure tips 86, the threads are locked,buried and trimmed, preferably as described previously. Thus, unlikeprior art tissue valves wherein leaflets are attached individually andthe peripheral stitching of the cusps terminates before the tips of thecommissures, producing a potential stress point, the method of thepresent invention produces a novel tissue valve assembly having uniformstitching from commissure tip to commissure tip and consistently alignedcoapting leaflet mating edges.

Attachment of the Tissue-Wireform Structural Assembly to a Support Stent

For purposes of further explanation, once the assembled tissue-wireformstructural assembly, which is identified by reference numeral 58, isproduced as discussed above, the assembly 58 is then attached to asupport or stent 56. Referring to FIGS. 9, 10, and 11, thetissue-wireform structural assembly 58 is first fitted onto thecorrespondingly configured stent 56 in a manner that will uniformlyclamp the peripheral cusp edges of the leaflets 68 between an uppersurface 99 (see FIG. 1) of stent 56 and the lower surface of wireform54. This assembly technique further distributes stresses and loads ofthe leaflets 68 and contributes to their functional longevity. Moreover,pre-alignment of the leaflets 68 and attachment to the wireform 54enables the dimensions of the entire valve 50 to be aligned at once andeliminates the dimensional variation that could occur in prior artvalves due to the utilization of separate commissure posts. Inparticular, stent 56 is dimensioned to mate or seat with theconfiguration of assembly 58, and assembly 58 is mated to stent 56 suchthat the lower surface of each commissure tip 86 of wireform 54 mateswith the top surface of a corresponding and complementary stentcommissure tip 100. Care is taken to ensure that central opening 102formed by coapting mating leaflets 68 is not distorted while matingtissue-wireform structural assembly 58 to stent 56. Similarly, care istaken to ensure that leaflets 68 are uniformly clamped and remain evenlytensioned throughout this process.

Once wireform assembly 58 is mated to stent 56, a temporary pin 104 canbe inserted at the bottom curve of each leaflet cusp 92 to temporarilysecure wireform assembly 58 to stent 56. Stent 56 and assembly 58 thenare sutured together as shown in FIGS. 10 and 11. Suturing of assembly58 to stent 56 begins at the tops of the commissure tips 86. Inparticular, a double-threaded needle (not shown) is inserted throughstent commissure tip 100 as indicated at 105', between free tab ends106, 108 of adjacent pairs of leaflets 68, and through cloth edge 84 ofwireform assembly 58 as indicated at 109". The needle is then insertedthrough the looped thread to form a single lock 110. A double lock 112is then formed, with the needle being inserted through stent commissuretip at 105" and through cloth edge 84 at 109", substantially in themanner previously discussed so that double lock 112 is able to be pulledunderneath cloth edge 84. Excess thread exiting from cloth edge 84 asindicated at 113 may then be trimmed and discarded. The identicalprocedure may be performed for the remaining commissure tips 86 of thewireform assembly 58. As a result, wireform commissure tips 86 evenlymatch with stent commissure tips 100.

With reference to FIGS. 9 and 12-14, the exemplary attachment procedurecan be completed by inserting a double-threaded needle as previouslydescribed through stent 56 near the top of stent commissure tip 100 asindicated at 114', through tissue leaflet 68 and through cloth edge 84of wireform 54 as indicated at 115'. The needle is then re-inserted in areverse manner through cloth edge at 115", through stent commissure tip100 at 114" and passed through loop 115 of the double thread. Withreference to FIG. 14, the suture is then tightened so that loop 115 ispositioned securely and firmly against stent commissure tip 100.In-and-out suturing 116 (see also FIGS. 15 and 16) is then performedalong the mating edges of stent 56 and wireform assembly 58 up to thenext wireform assembly and stent commissure tips 86, 100. With referenceto FIG. 13, at a position near the top of the commissure tip 86, asingle lock 118 and a double lock 120 can be formed, and the thread canbe buried beneath cloth edge 84 of wireform assembly 58 as describedpreviously. It will be appreciated that the suturing just described maybe initiated at any of the stent commissure tips 100 and that thein-and-out suturing 116 may be performed in either a clockwise or acounter-clockwise manner around the periphery of stent 56.

Upon completion of the in-and-out suturing 116 around the periphery ofstent 56, the free tab ends 106, 108 of each pair of tissue leaflets 68need to be secured to the respective stent commissure tip 100. Referringto FIGS. 15 and 16, two exemplary alternatives are provided to performthis task.

Referring to FIG. 15, a first exemplary alternative is to configure tabends 106, 108 to form a butt joint 122. In particular, tab ends 106, 108are trimmed such that, when folded towards each other, the respectiveend edges of each tab end 106, 108 mate evenly to form, preferably, astraight center line descending vertically from the top of commissuretip 100. The two leaflet tab ends 106, 108 are then stitched togetherwith stitching 124.

Referring to FIG. 16, a second exemplary alternative for securingleaflet tab ends 106, 108 is to configure tab ends 106, 108 to mateevenly to form a flush junction 126 with cloth edge 84 of wireform 54 oneither side of commissure tip 100. In particular, leaflet tab ends 106,108 can be trimmed so that the end edges of each tab 106, 108 are sizedto fit flush with cloth edge 84 of the wireform. Leaflet tab ends 106,108 are then stitched to cloth edge 84 of wireform 54 with stitching 128as shown. The alternative flush junction 126 so formed provides asomewhat flatter commissure than butt junction 122 of the firstalternative does, and, therefore, flush junction 126 may be moredesirable when a more compact valve is needed. Both exemplary methods,however, allow even and reliable distribution of the load on the tissueleaflets at the commissures.

Assembly of an Exemplary Stent

From the foregoing description, it will be appreciated that stent 56 isconfigured to have a structure suitable for mating and supportingwireform assembly 58. In that connection, an exemplary structure ofstent 56 will now be described with reference to FIG. 17. Those skilledin the art will appreciate that the exemplary stent described herein isa multi-piece construction. However, it is contemplated as being withinthe scope of the present invention to provide a single-piece stent.However, the multi-piece stent assembly illustrated may make it easierto engineer or fine tune the radial stability of the stent whilemaintaining desirable axial flexibility of the commissure posts. Thefirst step in the assembly of exemplary stent 56 is to fabricate aninner support member 130 and an outer support member 132, which, whenmated together, generally form the shape of stent 56 which ultimatelyconforms to the configuration of wireform assembly 58. In the exemplaryembodiments inner support member 130 is configured with three upstandingposts 134 that serve as the support structures for the stent commissuretips 100. Outer support member 132 also may include posts 136 thatcorrespond to the posts 134 of the inner support member 130. However,posts 136 are truncated and therefore do not match the height of posts134 on inner member 130. The inner and outer support members 130, 132may be fabricated from a metal or plastic material depending on thedesired characteristics of valve 50.

Disposed on inner support member 130 are a plurality of sewing holes 138along the periphery of member 130 and on the posts 134. The outersupport member 132 includes at least one sewing hole 139 on each of itstruncated posts 136 that correspond with respective ones of the sewingholes 138 on each post 134 of the inner member 130. The inner diameterof outer support member 132 is sized to form a slip fit with the outerdiameter of inner support member 130.

Inner support member 130 is placed within outer support member 132 suchthat sewing holes 139 of outer support member 132 align with sewingholes 138 on the respective posts 134 of inner member 130. The twomembers are then sewn together by inserting a double-threaded needle asdescribed previously through the aligned holes 138, 139. As shown inFIG. 18, thread 140 inserted through each of the aligned holes 138, 139is then passed through end loop 142 and tightened. The thread may thenbe locked using, for example, a slip knot (not shown), which is a knotthat may slide along the thread to abut the support members.Accordingly, posts 134 of inner support member 130 flex to a greaterextent from base portions thereof to tops thereof, and outer supportmember 132 augments the radial stability of inner support member 130,with the truncated posts 136 providing rigidity to base portions ofposts 134 of inner support member 130.

Referring now to FIG. 19, once the inner and outer support members 130,132 are sewn together, a covering cloth 144, preferably made from wovenpolyester, is cut and formed into a cylindrical tube for covering thecombined support members 130, 132. Those skilled in the art willappreciate that the covering cloth is equally applicable to single-piecestent assemblies. Covering cloth 144 includes two crease lines 146, 148,the first of which, 146, is formed from folding an edge of cloth 144 toform a fold which receives posts 134 of inner support member 130. Thereis approximately 1 mm to 1.5 mm between first crease line 146 and a topedge 149 (see FIGS. 17 and 18) of each post 134 in the exemplaryembodiment. Second crease line 148 is located such that it correspondsto a lower edge 150 (see FIG. 18) of combined support members 130, 132.

Referring now to FIG. 20, to secure covering cloth 144 to supportmembers 130, 132, a threaded needle may be inserted through cloth 144,through a hole 151 of one of inner member posts 134, through the secondlayer of cloth 144 and then back through cloth 144 through the same hole151 and through cloth 144. The needle then can be passed through a loopto form a first lock 152. This threading step may be performed up to twomore times. The excess thread is then trimmed and discarded. The sameprocedure can be followed for each of the three posts 134 on innersupport member 130.

Then, as shown in FIG. 21, the next exemplary step involves stitchingcovering cloth 144 to inner and outer support members 130, 132 along anupper edge 137 of inner support member 130. First, lower edge 154 ofcloth 144 can be folded into the interior of support members 130, 132along crease line 148 such that second crease line 148 defines the lowerend or bottom of the support member structure. This fold results indual-layered cloth 144 (including outer and inner cloth layers 156, 158)enveloping support members 130, 132. Then, using a single threadedneedle, the layered cloth is stitched together at 155 along thecurvature of the upper edge 153 of support members 130, 132. Thestitching 155 is preferably backstitching, which is accomplished byinserting the needle a stitch length, for example, to the right andbringing it up an equal distance to the left. However, the stitching 155does not extend to the tops 149 of posts 134, leaving a space ofapproximately 1 mm between the top 149 of post 134 and the stitching155. After stitching the upper edge 153 of support members 130, 132, thecloth 144 then can be stitched in a similar manner at 156 along thelower edge 150 of support members 130, 132. The last stitch is thenlocked by tying a slip knot, which may be performed up to three times tolock the stitching securely in place.

Referring now to FIGS. 21-26, cloth 144 as now attached to supportmembers 130, 132 is trimmed to conform to the shape of support members130, 132 and, if desired, to provide a gasket-like sewing edge. Toaccomplish this, outer cloth layer 157 can be sliced downwardly from atop edge thereof to a distance approximately 5 mm to 6 mm above the topedge 153 of inner support member 130. In a similar manner, inner clothlayer 158 can be sliced downwardly from a top edge thereof to a distanceapproximately 2 mm to 3 mm above the bottom of the slice in outer clothlayer 157. The slices are made at a location midway between adjacentposts 134 of inner member 130 and are intended to align with one anotherin the downward direction, as indicated at 160.

Next, outer cloth layer 157 can be trimmed along the upper edge 153 ofinner support member 130, starting at the bottom of the slice formed inouter cloth layer 157. In this exemplary embodiment of the presentinvention the trimming is performed in a manner such that the contour ofthe cloth 144 extends a distance of approximately 4 mm to 5 mm above thelower curved portions of the upper edge 153 of support member 130, adistance of approximately 2 mm to 3 mm above portions of support member130 in the areas at or near the base of posts 134 of support member 130and a distance of about 0.5 mm to 2 mm above the tops 149 of posts 134of support member 130.

As shown in FIG. 22, inner cloth layer 158 is then folded over the tops149 of posts 134 of inner member 130 and is anchored to posts 134 with athreaded needle stitched through sewing hole 151 in posts 134 in themanner previously described with respect to the upper folded section ofcloth 144. However, after these locking stitches are executed, theneedle is passed under the cloth so as to exit from the top of post 134.

Next, a series of trimming operations can be performed. Referring toFIGS. 22 and 23, a folded portion 162 of inner cloth layer 158 istrimmed around the entire circumference of the cloth so that lower edge164 of folded portion 162 is approximately 1 mm to 1.5 mm from thestitch in hole 151 of post 134. A folded portion 168 of outer clothlayer 157 is folded over the tops 149 of post 134 of inner supportmember 130. Folded portion 162 of the inner cloth layer 158 is furthertrimmed so that its remaining edges are flush with the edges of thepreviously trimmed inner cloth layer 158. With regard to the non-foldedportion of inner cloth layer 158, this layer is trimmed in a manner suchthat its edges extend approximately 2 mm beyond the edges of thepreviously trimmed outer cloth layer 157. The 2 mm extension of theinner cloth layer 158 beyond the outer cloth layer 157 provides thematerial desired to form a seating and attachment or sewing surface onthe stent.

Each of the trimming operations is performed starting from the centralarea between posts 134 of inner support member 130 to the tops 149 ofposts 134. The arrangements of inner cloth layer 158, outer cloth fold168, outer cloth layer 157 and inner cloth fold 162 are shown in theenlarged cross-section of FIG. 23.

The remaining exemplary step to complete the assembly of the stent 56 isto fold and suture the cloth layers to form a sewing edge 169 around thestent 56. Referring to FIG. 24, inner cloth layer 158 is folded aroundpost 134 and stitched so as to enclose post 134. More specifically, thethread previously inserted through the top of post 134 when connectingfolded outer cloth layer 157 through sewing hole 151 is now used tocreate first and second locks 172 on the top of post 134 so as to holdinner cloth layer 158 in place on the top of post 134. A wipstitch 174may then be utilized to further secure exemplary inner cloth layer 158downwardly around post 134 approximately 8 mm from the top of post 134.When the bottom of the post 134 is reached, first and second locks areformed, and the thread is trimmed and discarded. The above-describedstitching operation is performed for each of the three posts 134.However, for the last of the posts 134 to be stitched, instead oftrimming the thread after forming the first and second locks 172,untrimmed thread 176 can be used for performing the stitching of thecloth along the remaining edges of support members 130, 132 betweenposts 134.

In that connection, with reference to FIGS. 25 and 26, inner cloth layer158 is folded over the outer cloth layer 157, and an alternatingstitching is applied to hold the folded layers in place on the supportmembers and thereby to form the sewing edge 169 on the stent. Aftercompleting the stitching around the remaining portions of the supportmembers 130, 132, a first and second lock stitch can be formed with thethread, and the excess thread is trimmed and discarded to complete theassembled stent 56.

Assembly of an Exemplary Suture Ring

Where valve 50 is intended for use in the replacement of a native heartvalve, a soft suture ring 60 is contemplated for use in completing thevalve structure. For example, referring to FIG. 27, an exemplary ringwasher or "remey" 180 is provided which is preferably made fromnon-woven polyester. Also provided is a silicone sponge waffle annulus182 for mating with remey 180. In that connection, annulus 182 isconfigured to have a walled lip 184 configured to be disposed along theinner circumference 185 of remey 180. Lip 184 is contoured to includethree depressions 186 that correspond with the lower curved surfacesbetween each commissure on valve 50. Remey 180 mounts on waffle annulus182 such that remey 180 surrounds the walled lip 184. This produces asoft, relatively flexible, yet stable suture ring internal structurewhich, when covered with cloth as discussed below, functions as acompliant, stitchable interface between the natural tissues of the heartand the prosthetic tissue valve 50.

As shown in FIG. 28, before mounting remey 180 on waffle annulus 182, acloth 188 is positioned around remey 180 to extend from the innercircumference 185 to the outer circumference 189. Remey 180 is thenmounted on waffle annulus 182 such that cloth 188 is sandwiched betweenwaffle annulus 182 and remey 180. Cloth 188 is placed to extend adistance 190 of approximately 3 mm to 5 mm beyond the outercircumferential edge 189 of remey 180, as shown in FIG. 28. Remey 180,cloth 188 and waffle annulus 182 are then sewn together using, forexample, in-and-out suturing 192 around the circumference of remey 180.The exemplary suturing is preferably placed a distance 194 ofapproximately 1 mm from the outer circumferential edge 189 of remey 180.If desired, a second suture line (not shown) may be added at the samelocation as the first suture line, with each stitch of the second sutureline placed between the stitches of the first suture line. The resultingsuture 192 then appears as a continuous line of stitching. Additionally,as shown in FIG. 29, to further secure cloth 188 and waffle annulus 182together, back stitching 195 may be applied in the space between thewalled lip 184 of annulus 182 and remey 180, which space is indicated at196 in FIG. 28.

Referring now to FIG. 30, cloth 188 can be attached to depressions 186of the structural assembly of remey 180 and waffle annulus 182 with, forexample, a single-threaded needle inserted at one corner 198 ofdepression 186 (through cloth 188 and annulus 182) and then with adouble slip knot to secure the thread at corner 198. In-and-outstitching 200 can be then used to secure cloth 188 to the contour ofdepression 186. The same method can be followed for each depression 186.The excess cloth is then trimmed to the outer edge of remey 180 asindicated at 201.

With additional reference to FIG. 31, an outer portion 202 of cloth 188then can be folded around the external surfaces of remey 180 and tuckedunder remey 180 between remey 180 and waffle annulus 182. Because ofannulus 182 is pliant, annulus 182 deforms and accommodates the outerportion 202 of cloth 188. Using a single-threaded needle, an alternatingstitch 204 can be used to secure folded cloth 188 underneath remey 180.After completing the stitching of the entire circumference of remey 180,a double knot can be formed to secure the stitching, yielding a finishedsuture ring.

Attachment of the Suture Ring to the Exemplary Valve

Referring to FIGS. 32 and 33, to attach suture ring 60 or an alternativestructure such as flange 62 (see FIG. 1) to valve 50, depressions 186 ofsuture ring 60 are aligned with the descending peripheral cusps 206 ofvalve 50 and then mated together. More specifically, valve 50 is placedon suture ring 60 such that cloth edge 84 of the wireform 58 on thelower-most portion of each cusp on valve 50 is substantially flush witha top surface of suture ring 60 at corresponding depressions 186. Careis taken with the placement such that kinking or wrinkling of tissueleaflets 68 is avoided. Valve 50 can be temporarily pinned in place onsuture ring 60 with needles 208 to facilitate this procedure.

As shown in FIG. 34, the assembly of pinned valve 50 and suture ring 60can be flipped over, and suture ring 60 can be stitched to valve 50along mating edges 209 of ring 60 and valve 50. More specifically, inthe exemplary embodiment a single threaded needle can be used to sewsuture ring 60 to the cloth of the stent structure. To facilitate thestitching step, the pieces are held temporarily, yet securely in placewith additional needles 208. The opposite side of ring 60 and valve 50can be sewn together in a similar manner.

Attachment of Valve to Outflow Conduit

Referring now to FIGS. 35-37, in certain applications, it may bedesirable to attach valve 50 to an outflow conduit such as that shown at66. For example, in some patients requiring replacement of the aorticvalve, a portion of the aorta itself may be damaged or diseased suchthat it needs replacement as well. Accordingly, consistent with theteachings of the present invention, the adaptable tissue valve structurecan be modified to include an outflow conduit 66 that will function toreplace the damaged aorta. Alternatively, in some intended mechanicalpumping applications the adaptable tissue valve of the present inventionmay be provided with an outflow conduit to facilitate interfacing withthe mechanical pumping structure. In either alternative, this can beaccomplished as shown in FIGS. 35 and 36 where an outflow conduit 66 maybe attached to wireform 54 at the time that the tissue leaflets 68 arebeing secured. In particular, referring to FIG. 36, conduit 66 may besecured on a side of wireform 54 opposite to tissue leaflets 68 by, forexample, stitching. Alternatively, as shown in FIG. 37, conduit 66 maybe stitched and secured to wireform 54 on the same side as tissueleaflets 68, or sandwiched therebetween. A third option is to simplysecure conduit 66 to the periphery of the finished valve (not shown) asa subsequent sewing step. The valve 50 may be attached to an outflowconduit either with or without a sinus.

Alternative Configurations for Inflow Side of Valve

FIG. 38 illustrates additional exemplary alternative options availablefor modification and attachment of valve 50. For example, as discussedabove, when it is desired to use valve 50 as a conduit valve, suturering 60 may be attached to valve 50 as previously described.Alternatively, in applications such as artificial hearts or leftventricular assist devices (LVADs), suture ring 60 is not necessarilyrequired; hence, the lower end of stent 56 may be attached to flange 62for use in mounting the valve in the artificial heart or LVAD.

Yet a further alternative adaptation involves those applications wherean inflow conduit 64 is desired. In such applications, inflow conduit 64may be attached directly to stent 56 of valve 50. More specifically,inflow conduit 64 may be configured to have a stepped circumference 210that snugly mates with the outer periphery (or, alternatively, the innerperiphery) of stent 56 and which can be sewn thereto. In thisconfiguration, for example, in an artificial heart or an LVADapplication, suture ring 60 could be attached to inflow conduit 64rather than to valve 50.

Conclusion

In view of the foregoing description of exemplary embodiments of valve50 and the components thereof, the present invention satisfies the needfor improved tissue-type prosthetic heart valves in which stress isreduced on valve leaflets 68 while desirable structural and functionalfeatures are maintained. Additionally, valve 50 is adaptable for use ina variety of positions within the natural heart or in mechanical pumps.Further, valve 50 is simpler and easier to manufacture in a moreconsistent manner than existing valves.

The standardized leaflet structure subassembly 52 of the presentinvention can be modified readily to adapt to different intendedapplications. Of equal importance, leaflet subassembly 52 uniformlydistributes tensile loads along the entire periphery of leaflet cusps92, reducing stress points and significantly improving the long-termfunctionality of valve 50. As an added benefit of the present invention,the stability and adaptability of the tissue valve subassembly isachieved through simplified manufacturing processes utilizing fewersteps and subassemblies. This manufacturing protocol can be incorporatedinto branched, adaptable manufacturing techniques for the production oftissue heart valves having a variety of end uses. Further, theseimproved construction techniques expedite the overall manufacturingprocess and improve the consistency of valve 50 while simultaneouslyreducing the need for post-assembly fine tuning and quality-controlprocedures.

The plurality of tissue leaflets 68 being attached together as describedform the dimensionally stable and dimensionally consistent coaptingleaflet subassembly 52. Further, sutures 96 used to attach cusps 92 towireform 54 act like similarly aligned staples, all of which equallytake the loading force acting along the entire periphery of cusp 92 ofeach pre-aligned, coapting leaflet 68. The resulting tissue-wireformstructural assembly 58 reduces stress and potential fatigue at theleaflet suture interface by distributing stress evenly over the entireleaflet cusp 92 from commissure to commissure. Further, tissue-wireformstructural assembly 58 may be attached to cloth-covered stent 56 withoutdisturbing leaflets 68 or disturbing their relative alignment and theresultant coaptation of their mating edges.

Stent 56 as fabricated according to the present invention providesevenly distributed support and dimensional stability for each leaflet 68of the valve structure 50 from commissure to commissure. This assemblymethodology allows the evenly sutured tissue of leaflet cusps 92 to besandwiched between wireform 54 and stent 56 and to thereby furtherdistribute the loading forces more evenly around the attachment site.Because leaflets 68 experience lower, more evenly distributed stressesduring operation, leaflets 68 are less likely to experience distortionin use. Thus, a more stable, long lived, functional closure orcoaptation of leaflets 68 is provided by this even distribution ofattachment forces.

Furthermore, for each key area of stent 56, the flexibility can beoptimized or customized. If desired, the coapting tissue leafletcommissures 86 can be made more or less flexible to allow for more orless deflection to relieve stresses on the tissue at closing or to finetune the operation of valve 50. Similarly, the base radial stiffness ofthe overall valve structure can be increased or decreased to preservethe roundness and shape of valve 50. Unlike a rigid mechanical valve,stent 56 does not act as a rigid heart valve structure but as a radiallystable, yet axially flexible support. A rigid structure is unnecessaryby utilizing the teachings of the present invention because leaflets 68are dimensionally pre-aligned along their mutually coapting mating orsealing edges 70 prior to being directly attached to cloth-coveredwireform 54. As a result, the entire sealing aspect of valve 50 can bealigned in three dimensions at once without the variability previouslyexperienced in the construction of prior art tissue-type valves. Inaddition to eliminating the need for post-assembly adjustment, thispre-alignment provides for consistency and simplicity in the manufactureof valve 50. Further, wireform 54 functions as a template for suturingleaflet cusps 92 to the valve subassembly with uniform stitching fromcommissure tip 86 to commissure tip 86. This produces a dimensionallyconsistent structure that can interface with stent 56 in a previouslyunobtainable uniform manner. The consistent dimensional integrity ofleaflet wireform subassembly 58 enables stent 56 to function as a stressrelieving support clamp which further secures leaflet cusps 92 in valve50 to provide an added degree of stability and stress distribution. Ifdesired, providing the top 99 of the stent 56 with a single or doublefold of covering cloth 144 provides the stent lip with a deformablecloth seat that assists in the distribution of load around leaflet cusps92 and simplifies sewing stent 56 to tissue-wireform structuralsubassembly 58. Those skilled in the art will appreciate that attachingstent 56 to tissue-wireform structural subassembly 58 functions tostabilize the projecting commissure posts of the valve subassemblywithout stiffening their desirable axial flexibility. This novelconstruction technique eliminates the need for separate commissure postsat the tissue leaflet commissures and also eliminates multiple tissueand cloth layers at wireform commissures 86 which adds to uniformity andconsistency in valve production and eliminates assembly steps. As aresult, valve manufacture is not only improved, but simplified andexpedited as well.

Stent 56 also functions as an adaptable structural interface, allowingthe tissue-wireform-stent structural subassembly to be attached to avariety of additional structures dependent upon intended valve placementand operating environments, including soft suture ring 60, mechanicalflange 62, inflow conduit 64, and outflow conduit 66. Unlike prior arttissue heart valves, the present invention provides this flexibility andadaptability of use because key valve components can be standardized fordifferent types of valves or valve applications. This manufacturing andstructural consistency also improves quality control and providesrepeatability and consistency in the formation of the valves. It alsosimplifies final assembly that in turn provides for increased productionrates without sacrificing consistent product quality.

As part of the flexibility of the present invention, stent 56 may bedesigned to be adaptable so that different ways of attaching valve 50 tovarious intended applications can be accommodated. The novelconstruction that allows for this universal application results fromstent 56 providing a complete uniform support to the dimensionallystable, pre-aligned wireform/leaflet subassembly 58. Because of thisadaptability, valve 50 can function in a variety of applications,including that of a temporary heart valve prosthesis within acirculatory support system using a relatively rigid flange or a conduitassembly rather than a standard soft sewing ring. Alternatively, valve50 can function as a prosthetic valve having a soft, scallop-shapedsewing ring for aortic positioning or a soft flat sewing ring for mitralpositioning, or as a conduit valve by incorporating proximal and distalconduits attached on both the inflow and outflow valve ends. The outflowconduit can have a sinus shape to improve blood flow if desired. Withinan artificial heart system, valve 50 mimics the hemodynamic pumpingaction of the heart while sustaining the patient until a donor heart islocated and successfully transplanted. In this application, both bloodinflow and outflow functions can be accommodated by valve 50.

From the foregoing detailed description, it will be evident that thereare a number of changes, adaptations and modifications of the presentinvention which come within the province of those skilled in the art.However, it is intended that all such variations not departing from thespirit of the invention be considered as within the scope thereof aslimited solely by the claims appended hereto.

What is claimed is:
 1. A method of making a tissue leaflet subassembly for use in a heart valve, said method comprising the steps of:providing sheet-like tissue; providing a planar template having a pair of oppositely directed tabs, a substantially linear edge extending between said tabs, and a substantially arcuate portion extending between said tabs; placing said template on said tissue; and cutting away portions of said tissue which extend beyond said template to form a tissue leaflet having a pair of opposing faces, a pair of oppositely directed tabs, a substantially straight edge extending between said tabs, and a substantially arcuate cusp edge extending between said tabs; repeating the preceding steps to form a plurality of tissue leaflets; attaching the tabs of said tissue leaflets to each other to form said tissue leaflet subassembly.
 2. The method of claim 1 wherein:said template has a guide slot formed in the linear edge; and said attaching step includes the steps of:aligning said template with a first two of said tissue leaflets, the first two tissue leaflets contacting one another; and inserting a needle with thread through said guide slot and through said first two tissue leaflets to attach one adjacent pair of tabs of the two leaflets, the other pair of adjacent tabs being left unconnected; and securing said thread.
 3. The method of claim 2 wherein there are three leaflets in the tissue leaflet subassembly and the method further includes:aligning said template with a third one said tissue leaflets; separating the unconnected adjacent tabs of the two leaflets and aligning each separated tab with one of the tabs of the third leaflet; and inserting a needle with thread through said guide slot and through said aligned tabs to complete the formation of the tissue leaflet subassembly.
 4. A method of assembling an adaptable, tissue-type heart valve, said method comprising the steps of:forming a dimensionally stable, pre-aligned tissue leaflet subassembly from a plurality of substantially identical tissue leaflets defining a subassembly peripheral edge; providing a generally circular wireform having a bottom surface dimensioned to receive said dimensionally stable, pre-aligned tissue leaflet subassembly peripheral edge in mating engagement; providing a generally circular support stent having an upper surface dimensioned to engage said dimensionally stable, pre-aligned tissue leaflet subassembly peripheral edge; and clamping said dimensionally stable, pre-aligned tissue leaflet subassembly peripheral edge between said wireform bottom surface and said support stent upper surface.
 5. The method of claim 4, further comprising the additional step of attaching said dimensionally stable, pre-aligned tissue leaflet subassembly peripheral edge to said bottom surface of said wireform prior to said clamping step.
 6. The method of claim 5 wherein said clamping step comprises the additional steps of:engaging said upper surface of said support stent with said attached dimensionally stable, pre-aligned tissue leaflet subassembly peripheral edge; and attaching said support stent to said dimensionally stable, pre-aligned tissue leaflet subassembly peripheral edge and to said wireform.
 7. The method of claim 6 wherein said attaching step comprises sewing.
 8. The method of claim 4 further comprising the additional step of attaching an adaptable structural interface to said support stent after said clamping step.
 9. A method of assembling a tissue heart valve, said method comprising:forming a leaflet subassembly by:providing three tissue leaflets, each of the leaflets having a pair of opposing tabs, a coapting edge extending between the opposing tabs, and a substantially arcuate cusp extending between the opposing tabs and having a peripheral edge; mating and attaching each of the opposing tabs of each of the leaflets to a respective one of the opposing tabs of another of the leaflets, with each leaflet being attached to one tab of each of the other two leaflets, the mating leaflet tabs projecting outward therefrom; providing a wireform having three commissures defined by two spaced apart wire sections joined at a tip, and three arcuate portions extending between adjacent pairs of the commissures, the wireform being complementary to the leaflet subassembly in size and arrangement such that each of the commissures corresponds to one of the pairs of mating leaflet tabs and that each of the arcuate portions corresponds to the arcuate cusp of one of the leaflets of the leaflet subassembly; positioning the wireform over the leaflet subassembly with the mating leaflet tabs positioned adjacent the tip between the two spaced apart wire sections of the commissures and the arcuate portions juxtaposed with the arcuate cusps; and attaching the leaflet subassembly to the wireform at the commissures and along the arcuate portions to form a leaflet/wireform subassembly.
 10. The method of claim 9, wherein the wireform is cloth-covered and the step of attaching the leaflet subassembly to the wireform comprises suturing the leaflets to the cloth covering.
 11. The method of claim 10, wherein the cloth-covered wireform has a cloth edge and the leaflet subassembly is sewn to the cloth edge of the cloth-covered wireform.
 12. The method of claim 9, further comprising:providing a generally circular support stent having upwardly extending flexible commissure posts and an upper surface, the leaflet/wireform subassembly having a complementary bottom surface; engaging the support stent upper surface to the bottom surface of the leaflet/wireform subassembly attaching the mating leaflet tabs to the stent commissure posts.
 13. The method of claim 12, wherein the stent commissure posts are positioned radially outside of the wireform commissures, and wherein the method includes:attaching each pair of mating leaflet tabs at locations spaced from their respective radially outermost ends; after forming the leaflet/wireform subassembly, separating the pair of tab ends outside of the spaced apart wire sections of the commissures; and passing each separated tab end on opposite sides of the associated stent commissure and attaching them thereto so as to induce clamping of the leaflet tabs between the stent commissure posts and wireform commissures upon a radially inward force being applied to the leaflets.
 14. The method of claim 13, including passing each separated tab end around the outside of the associated stent commissure post and rejoining the tab ends at a stitched butt joint. 